Market Segmentation strategy is a lot easier on the web than most would consider. In the past, advertisers would have to bid on traditional media space in order to market to specific markets. If you were selling Count Chocula, you would have to be in children's magazines or advertise during children's programming time slots. If you're selling pharmaceutical drugs, you'll have to wait for adult programming. It's not as effective in the traditional market space because you might be trying to sell a toy geared more towards a boy and maybe half the viewers are automatically disqualified because they're girls. Even though you're paying for 1 million views, only 500K are qualified for your product. That's a tremendous reduction for what you were looking to do.
On the web, it's much easier to segment, especially if you're a webmaster. If you have a website that you're required to sign in with an account, you can gather details about your users and segment based on age, gender, location, interests, etc... It's very valuable to segment out your viewership because you can charge higher rates to advertise. Essentially the more you can segment, the higher you can charge. In theory, if you really wanted to reach one person to advertise to you, you can charge them a fortune because that's some uber-specific criteria that only you're privy to generating.